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The spider family Trechaleidae includes 120 described species, just one of which (Trechalea gertschi) occurs in North America north of Mexico, with a range extending from Sonora and Chihuahua in Mexico into portions of the Gila River drainage in Arizona and New Mexico. This family is limited almost entirely to the New World tropics. (Carico 2005; Platnick 2014). Carico (2005) briefly reviewed the taxonomic history of the trechaleids.
Trechalea gertschi is a relatively large, crablike spider. The body is moderately flat, with long legs that are held in a somewhat crablike stance. In the southwestern United States, these spiders are found at the margins of permanent streams and are typically seen perched head-down on the surfaces of rocks near the water margin. They readily run across the water surface and occasionally crawl underwater by walking down the surface of a partly submerged rock, behaviors seen in many North American Dolomedes (family Pisauridae), which T. gertschi closely resembles (although the posterior eye row is much straighter than in T. gertschi than it is in Dolomedes). Females carry the flattened, two-valved egg sac with their spinnerets and spiderlings ride on the upper surface of the sac upon emergence. (Carico 2005; Bradley 2013)
Nuptial courtship gift-giving in several Paratrechalea species has been the focus of a number of studies (Costa-Schmidt et al. 2008; Albo et al. 2009; Albo and Costa 2010; Klein et al. 2012; Disconzi Brum et al. 2012; Costa-Schmidt and Machado 2012; Klein et al. 2014).